The activation of the Uq transposable element system following an RNA virus infection led to the identification of severl Uq controlled mutants in maize. With the same treatment, activation and mobilization of two other systems (Bs1 and Tz86) was later observed. Of the three virus activated transposable element systems, only the Uq system is genetically characterized. Based on the sequence data for Bs1 and Tz86, elements belonging to the Uq system are expected to lack the terminal inverted repeats common to plant transposable elements and instead may be expected to exhibit a proretrovirus-like structure. The wide distribution of genetically active Uq elements in populations of diverse origin and the maintenance of these elements in breeder lines suggest that this system plays an evolutionary role by creating genetic variability in maize. The Uq transposable element system contains two classes of elements. These are distinguished genetically based on their expression of transactive functions necessary for element excision. The Uq elements express thes functions, while the rug elements require these functions in trans. Currently the only elements belonging to this system available for molecular study are the ruq elements at the A and C loci. This project is designed to genetically locate phenotypically distinct Uq transposable elements at cloned gene loci in maize for their eventual molecular characterization. It will use a field screening method proven highly successful with the En system to isolate new transposable element induced mutations and identify the element (predicted to be Uq) located within the mutant allele. With the localization of several unique Uq elements at known lici, Uq regulatory functions which affect the frequency, developmental timming, and tissue specificity of excision events may be studied in moe depth. Molecular study of those functions necessary for Uq controlled transposition, including an examination of the Uq transcripts, would allow an investigation of the virus activation mechanism. Following the recovery of the Uq containing pericarp mutant, application of methods used to study Mp transposition events in the P-Mp system will allow the study of the Uq transposition mechanism.